Simple Music Handler

MusicHandler.client.lua

local SoundService = game:GetService("SoundService")

local Sound do
	Sound = Instance.new("Sound")
	Sound.Name = "Music"
	Sound.Parent = SoundService
end

local SongIndex = 1
local Songs = {
	"rbxassetid://5807578490",
	"rbxassetid://5410086218"
}

local function ChangeSong()
	Sound.SoundId = Songs[SongIndex]
	
	if Sound.IsLoaded == false then
		Sound.Loaded:Wait()
	end
	Sound:Play()
	
	SongIndex = SongIndex >= #Songs and 1 or SongIndex + 1
end

ChangeSong()
Sound.Ended:Connect(ChangeSong)